Question 987534
{{{ 3*( x + 21 )  = -4*( x - 21 ) }}}
Use distributive law which says:
{{{ a*( b + c ) = a*b + a*c }}}
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{{{ 3x + 63 = -4x + 84 }}}
Add {{{ 4x }}} to both sides
{{{ 7x + 63 = 84 }}}
Subtract {{{ 63 }}} from both sides
{{{ 7x = 21 }}}
Divide both sides by {{{ 7 }}}
{{{ x = 3 }}}
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check solution:
{{{ 3*( 3 + 21 )  = -4*( 3 - 21 ) }}}
{{{ 3*24 = -4*( -18 ) }}}
Divide both sides by {{{ 6 }}}
{{{ 3*4 = -4*( 3 ) }}}
{{{ 12 = 12 }}}
OK